The Prize:
The 1918 Nobel Prize in Chemistry to Fritz Haber for the “synthesis of ammonia from its elements.”
The Science:
Nitrogen is an important component of the rich, fertile soil needed for growing crops, though farming also depletes fields of this nutrient through plant uptake, leaching, and soil erosion. Farmers traditionally used crop rotation to maintain nitrogen levels in the soil, but by the early 20th century, farmers had responded to increased food demands with high-yield, single crop farming. Such farming practices require more nitrogen than can be fixed in the soil naturally. Stores of nitrate discovered in Chilean mines temporarily fed the agriculture industry’s appetite for nitrogen, but fears that the mines would run dry had many chemists wondering how to produce fertilizers chemically.
Nitrogen gas makes up over 78 per cent of our atmosphere but is relatively unreactive due to its strong triple-bond molecular structure. Chemists in the early 1900s struggled to use this vast source of elemental nitrogen to produce more useful nitrogen compounds like ammonia, a complex of nitrogen and hydrogen (NH3).
The first chemist to achieve this feat was the German chemist Fritz Haber. In 1909, Haber revealed the first Haber Synthesis machine, a “table-top” apparatus (engineered with the help of Robert Le Rossignol) that produced liquid ammonia at the rate of a cup every two hours. Once produced, ammonia can be oxidized to produce the nitrites that are useful as fertilizers.
The Haber synthesis of ammonia (NH3) from atmospheric nitrogen (N2) and hydrogen (H2) requires some extreme conditions: high pressure (~250 atmospheres), high temperature (~500˚C), and that the entire reaction happen over an iron catalyst. Even under these optimized conditions, the reaction is inefficient in terms of the amount of ammonia it produces, though the reaction is also exothermic, meaning that it releases energy on formation and this energy can then be captured and recycled to heat the un-reacted N2 and H2 continuing the process.
In 1913, the German chemical company BASF began industrial production of ammonia based on the Haber method. BASF enlisted Carl Bosch to convert Haber’s model to an industrial scale and Bosch subsequently won a Nobel in 1931 for his work. Today the industrial-scale reaction is known as the Haber-Bosch process.
The Significance:
Inexpensive, readily available ammonia changed the world of agriculture. The adaptation of modern agriculture to methods that require the use of nitrogen-rich fertilizers has been dubbed the “green revolution.” The high-yield production of corn, rice, and other food staples led many countries (including India and Mexico, which had previously been facing famine) to become agriculturally independent. Today, fertilizer manufacturers produce over 100 million tons of ammonia annually through the Haber-Bosch process. It is currently estimated that over one third of the global population relies on the Haber synthesis for its food.
The Haber-Bosch process also has a controversial side. Scaling-up the Haber process to an industrial level enabled Germany to mass-produce an artificial alternative to Chile saltpetre, the key ingredient in gunpowder at the time. During the First World War, the Triple Alliance controlled almost all the Chile saltpeter in the world, as most of the mine owners were British. Germany diverted most of the ammonia produced in its factories into synthetic Chile saltpeter and then into munitions. The Haber-Bosch process kept Germany in the war for years longer than would otherwise have been possible.
What you may not know:
Many were surprised when the Nobel was awarded to Haber in 1918. After developing the method to fix nitrogen, Haber joined the German war effort. Under Haber’s management, Germany developed its chemical warfare program and he personally witnessed the first use of poison gas at Ypres, Belgium in 1915. It is thought that his wife, also a chemist, committed suicide in reaction to Haber’s promotion of poison gas. Haber had a very successful career in chemistry in Germany, but in 1933 he was forced to step down from his position as a result of anti-Semitic Nazi laws. He died shortly afterwards.
